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Video Conferencing

frame estimation motion frames

Definition: Video conferencing allows participants in a live session to see each other; the video is transmitted over the network between users, live and in real time.

Video conferencing is one component of teleconferencing, the others are audio conferencing, and data conferencing. Since the video must be encoded, transmitted, and decoded in real-time, special compression and transmission techniques are typically used. In a teleconferencing system that is ITU-T H.323 compliant, the H.261video codec in its QCIF format must be supported. Support for other H.261 formats or the H.263 codec is optional. During the initial setup, a specific video data rate is selected during the capability exchange. This rate should not be violated throughout the duration of the session. The H.261 standard uses communication channels that are multiples of 64 kbps, known as p×64, where p [1, 2, 3, 30]. From a video encoding perspective, there are no Bidirectional or ‘B’ frames in H.261. Instead, it uses Intra or ‘I’ frames which are fully and independently encoded, and Predicted or ‘P’ frames which code the difference between the frame and its previous frame by using motion estimation.

Compared to H.261, H.263 uses 1/2 pixel motion-estimation for better picture quality, and a Huffman coding table that is optimized specifically for low bit rate transmissions. H.263 defines more picture modes than H.261, as seen in table 1 below. In addition, H.263 introduces the PB frames, which consist of a P frame interpolated with a Bidirectional or ‘B’ frame: a frame that depends not only on a previous frame but also on a forthcoming frame. Similar to a P frame, a B frame uses motion estimation to reduce the amount of information to carry. See the related article on ,Video Compression and Coding Techniques- and ,Motion Estimation for further details.

Video Content Analysis Using Machine Learning Tools - Introduction, Overview of Machine Learning Techniques [next] [back] Video Coding Techniques and Standards - Introduction, The need for compression, Perceptual Redundancies, The Human Visual System, Sensitivity to Temporal Frequencies

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